Blue diamond: Although she does care about her sister, the fact that the two of them share very different points of view can often cause them to argue and disagree with each other. After Blue diamond fell in love with the Iron giant, Yellow diamond told her sister that she must reject this relationship. In the end Blue obeys Yellow and she breaks up with the Iron giant. Despite that the blue gem broke the law, Yellow diamond promised to not expose her to either Toffee or the Horned king, because she knew that if she does, her sister would receive severe punishments.

trivia:

Most of the time, with the help of her powers, she is much shorter than a diamond is supposed to be, but still taller than most humans. When she is in her true height, she is as tall as a titan.